This site is another excellent resource from Dean Johnston (see also his Symmetry resource). It uses JSmol (in a web browser) to display different types of "Packing" and "Point Groups". For Packing, users can select different sizes for the atoms, display multiple unit cells, and rotate the model on the screen. Different layers can be color highlighted.
Other portions of the website include resources for incorporating crystallography into the undergraduate curriculum.
I use the Packing Models as part of a homework assignment in which they are stepped through multiple models. The Packing models displayed are very straightforward to manipulate and I would not worrying about having first-year students interact with it. I have not used the Point groups portion yet, but I intend to share that with students who are learning symmetry.
As with some other JSmol-based models, atomic radii are used instead of ionic radii so the traditional color coding (yellow for sulfur, red for oxygen, gray for metal) will suggest for some models that the anions are smaller than cations. In my assignments, I have students evaluate how well that agrees with tables of ionic radii.
It can be used in any modern web browser that supports HTML5 and/or Java. I have accessed models successfully on my iPhone, though it is much easier to use on a larger screen.